1. Field of the Invention
The invention relates to vehicle suspension systems, and in particular to suspensions for semi tractor-trails incorporating single-piece, cast trailing arms.
2. Description of the Related Art
Trailing beam suspensions for semi tractor-trailer combinations are well-known in the trucking industry. The typical trailing beam suspension comprises a hanger bracket suspended from a trailer frame rail. A trailing beam or arm is pivotably connected at one end to the hanger bracket to enable the trailing beam to pivot about a horizontal axis. The pivotable connection may comprise a resiliently bushed connection. The free end of the trailing beam is attached to a spring that is, in turn, attached to the trailer frame rail for cushioning the ride. The spring can comprise a mechanical spring, such as a coil spring, or an air spring. An axle is attached transversely to a pair of trailing beams on either side of the trailer through a rigid or resilient axle-to-beam connection. Other suspension and braking components can be attached to the trailing beam and/or the axle, such as a brake assembly, track bars, and shock absorbers.
Trailing beams can take a variety of shapes and cross sections, and are typically fabricated by welding individual components into the final assembly, thereby providing a beam with a hollow cross section. An example of such a beam is disclosed in U.S. Pat. No. 5,366,237 to Dilling et al. Such beams are typically designed for the maximum stress to which the beam will be subjected at any point on the beam. This approach results in sections of the beam having more material than is necessary for the maximum stress imposed on the beam at that section. This excess material adds to the cost and weight of the beam. Moreover, the welds induce stresses into the beam that can contribute to premature failure of the beam. Weld-induced stresses can be minimized by laying down welds that are of a consistent thickness. However, such detailed welding techniques can also increase the cost of fabrication and the weight.
Attachment of the axle to the beam is typically through some type of welded connection, such as disclosed in U.S. Pat. No. 5,366,237 to Dilling et al. Welded connections can induce in the axle stresses and cracks that can contribute to premature failure of the axle. Weld-induced axle stresses can be minimized by limiting the welded area to the region around the axle's neutral axis, and by starting and ending the weld at the same point on the axle. Moreover, the extent and location of the weld can preclude separation of the axle from the beam, which would be desirable in order to replace a damaged axle or beam without replacing the entire suspension.
Heretofore, resilient bushings have been utilized within the pivotable connection between the beam and the associated hanger bracket. It is also known to use bushings that have apertures extending along the length thereof to alter the spring-rate of the bushing along a particular path. Typically, these apertures are provided in pairs juxtaposed across the bushing. The bushing is then placed within the associated beam with the apertures vertically oriented, thereby altering the spring rate of the bushing for lateral shift of the trailer as compared to the spring rate for the bushing for roll of the trailer. In operation, these bushings are fixed with respect to the beams and pivot about pivot pins that are fixed with respect to the associated hanger brackets. However, these bushings can sometimes rotate with respect to the beam rather than the hanger bracket, thereby changing the orientation of the busing, and the orientation of the apertures located therein, and changing the direction in which the bushing affords a reduction in the spring-rate.
In previously known systems, significant wear of the trailing arms may occur proximate the hanger brackets during operation of the associated suspension system. Specifically, in many systems the roll of the vehicle causes the beams to shift within and contact the respective hanger brackets in a location about the periphery of the aperture of each beam within which the bushing are located. These areas about the aperture are typically constructed as thin as possible in an attempt to reduce the overall weight of each beam. The contact between the beams and hanger bracket causes excessive wear requiring the replacement of the beams to avoid catastrophic failure of the beams and/or bushings.
As discussed above, it is known to utilize bushings within the pivotable connection between the beams and hanger brackets, wherein the bushings include apertures extending through the bushings and oriented so as to alter the spring rate in a particular direction of compression while not effecting the spring-rate in others. However, the construction of these specialized bushings is more expensive than bushings that do not include such apertures. Moreover, the specialized bushings require proper orientation of the bushings with respect to the beams at all time, as discussed above.
Heretofore, maintenance of bushings associated with the pivotable connection between the beams and hanger brackets, i.e., the removal of the bushings from within the beams, has required the use of a specialized tool that abuts or engages the area of the beam near the bushing receiving aperture during extraction or installation of the bushing. As discussed above, these areas are typically quite thin in an effort to reduce the overall weight of each beam, thus providing only small areas for abutment of the tool.
During operation of the associated suspension system, bending stress are exerted on the axles, with localized points of stress being exerted at the locations of the connection between the trailing arms and the axles, thereby contributing to excessive stress on the axles and decreasing the useful life of the axles. Normal operation of the suspension system also leads to wear of the boot of the air spring each time the boot is allowed to contact the associated beam. This wear of the boot is especially prevalent during times of loading/unloading when air is not being supplied to the air springs.
Another cause of significant stress within previously known beam configurations, is the concentration of the upwardly directed load bear force exerted by the axle on the beam, and the downwardly directed forces exerted on the ends of the beam by the hanger bracket and air spring. This bending of the each beam results in a compressive force being exerted on the axle and the connection between the beams and the axle.
A configuration for a trailing arm or beam is desired that increases the lifespan of the beam within normal operating conditions, results in a beam having reduced weight while simultaneously providing increased structural integrity and a reduction to production and operating costs.